The human immunodeficiency virus (HIV-1) causes AIDS in man. Its simian counterpart (SIV) induces an AIDS-like disease in Asian monkeys. The development of an animal model system for infection and disease by HIV-1 is essential for AIDS vaccine studies and intervention. Currently, the only animal species which can be infected by HIV-1 is the chimpanzee; however, no disease is produced. Due to the enormous cost of maintaining a chimpanzee and the fact that this cannot be a disease model, a better model was sought. Based upon a recent report from the Washington Primate Research Center, we undertook studies to investigate HIV-1 infection in pig-tail monkeys. Initially, we are testing infectivity of pig-tail PBLs in vitro using various HIV-1 isolates including field isolates (< 4 passages) as well as some laboratory- adapted strains. Since the majority of North American HIV-1 isolates are "MN"-like in the V3 loop of the env region, our aim is to vaccinate and demonstrate protection against an "MN"-like HIV-1 isolate.